Urea solution injection device

ABSTRACT

The purpose of the present invention is to provide an exhaust purification device that is capable of adding an appropriate amount of urea solution without the need to directly measure the NOx emissions amount using an NOx measuring means. The exhaust purification device uses urea solution as a reducing agent for reducing nitrogen oxides within exhaust, and is provided with a temperature sensor, a humidity sensor, and a control device. A map is stored in the control device, and in said map the real NOx emissions amount for each rotation speed and each load of an engine occurring at a predetermined air temperature and a predetermined absolute humidity are converted using a correction formula into a reference NOx emissions amount for each rotation speed and each load of the engine while in a standard state. Using the map, the control device calculates a reference NOx emissions amount that corresponds to the rotation speed detected by a rotation speed sensor and to the load detected by a load sensor, uses the correction formula to convert the reference NOx emissions amount into the real NOx emissions amount occurring at an air temperature and an absolute humidity, and calculates a urea solution addition amount.

TECHNICAL FIELD

The present invention relates to an exhaust purification apparatus.Especially, the present invention relates to a urea solution injectiondevice for a ship.

BACKGROUND ART

Conventionally, an exhaust purification apparatus is known in which aselective reducing type NOx catalyst (SCR catalyst) is arranged insidean exhaust pipe and NOx (nitrogen oxide) is reduced into nitrogen andwater with ammonia as a reducing agent for decreasing the NOx in exhaustgas discharged from an internal combustion engine.

A urea solution is supplied from a urea solution injection nozzlearranged inside an exhaust pipe to exhaust gas, and ammonia is generatedfrom the urea solution by heat of the exhaust gas so as to reduce NOxinto nitrogen and water.

In the exhaust purification apparatus, when an addition amount of theurea solution against a NOx discharge amount is insufficient, NOx cannotbe decreased to a target purification rate (denitration shortage). Whenthe addition amount of the urea solution against the NOx dischargeamount is excessive, NOx in the exhaust gas is decreased more than thetarget purification rate (over-denitration) and ammonia slip thatammonia exceeding a theoretical equivalent is discharged to theatmosphere occurs. Then, there is a configuration that a NOx sensor isprovided in an exhaust pipe and control is performed so as to add theurea solution of a suitable amount against the NOx discharge amount. Forexample, it is like the Patent Literature 1.

However, in the NOx sensor of the exhaust purification apparatusdescribed in the Patent Literature 1, accurate measurement of the NOxdischarge amount may not be performed because of interference ofammonia. It is disadvantageous that the NOx sensor in the internalcombustion engine which is operated for 24 hours such as an engine for aship requires frequent maintenance work because of a short life of theNOx sensor.

PRIOR ART REFERENCE Patent Literature

Patent Literature 1: the Japanese Patent Laid Open Gazette 2008-157136

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

The present invention is provided in consideration of the problems asmentioned above, and the purpose of the invention is to provide anexhaust purification apparatus which can add a urea solution of asuitable amount without measuring directly a NOx discharge amount with aNOx measurement means.

Means for Solving the Problems

The problems to be solved by the present invention have been describedabove, and subsequently, the means of solving the problems will bedescribed below.

According to the present invention, an urea solution injection device ofan exhaust purification device in which an urea solution is added as areducing agent to exhaust gas of an internal combustion engine so as toreduce nitrogen oxide in the exhaust gas, includes a temperature sensordetecting a temperature of atmosphere, a humidity sensor detecting anabsolute humidity or a relative humidity of the atmosphere, and acontrol device calculating an addition amount of the urea solution. Amap, which converts an actual NOx discharge amount of the internalcombustion engine driven with each rotation speed and each load underpredetermined temperature and absolute humidity of the atmosphere intothe standard NOx discharge amount of the internal combustion engine witheach rotation speed and each load under standard conditions with acorrection formula is stored in the control device. A rotation speeddetection means detecting the rotation speed of the internal combustionengine and a load detection means detecting the load of the internalcombustion engine are connected to the control device. The standard NOxdischarge amount corresponding to the rotation speed detected by therotation speed detection means and the load detected by the loaddetection means is calculated with the map, the standard NOx dischargeamount is converted into the actual NOx discharge amount of the rotationspeed and the load under the temperature of the atmosphere detected bythe temperature sensor and the absolute humidity of the atmospheredetected by the humidity sensor with the correction formula by inverseoperation, and the addition amount of the urea solution is calculatedbased on the actual NOx discharge amount.

According to the present invention, the addition amount is calculated inconsideration of a target purification rate and a concentration of theurea solution.

Effect of the Invention

The present invention brings the following effects.

According to the present invention, the NOx discharge amount based onthe characteristic of the internal combustion engine can be calculatedwhile considering the temperature of the atmosphere and the absolutehumidity of the atmosphere which influence the NOx discharge amountgreatly. Accordingly, the urea solution of the suitable amount can beadded without measuring directly the NOx discharge amount with a NOxsensor.

According to the present invention, the addition amount of the ureasolution can be adjusted corresponding to the operating condition.Accordingly, the urea solution or ammonia of the suitable amount can beadded without measuring directly the NOx discharge amount with a NOxsensor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing of an exhaust purification apparatus according to anembodiment of the present invention.

FIG. 2 is a drawing partially in section of a urea solution injectionnozzle of the exhaust purification apparatus according to the embodimentof the present invention.

FIG. 3 is a flow chart of control processes of an addition amount of aurea solution according to the first embodiment of the presentinvention.

FIG. 4 is a graph of a relation between an actual NOx discharge amountand the addition amount of the urea solution.

DETAILED DESCRIPTION OF THE INVENTION

An explanation will be given on an exhaust purification apparatus 1according to an embodiment of the present invention referring to FIGS. 1and 2. In this embodiment, an “upstream side” means an upstream side ina flow direction of fluid, and a “downstream side” means a downstreamside in the flow direction of the fluid. The exhaust apparatus is notlimited to this embodiment and may alternatively be an air-less typeapparatus which does not use pressurized air.

As shown in FIG. 1, the exhaust purification apparatus 1 purifiesexhaust gas discharged from an engine 20. The exhaust purificationapparatus 1 is provided in an exhaust pipe 21 of the engine 20. Theexhaust purification apparatus 1 has a urea solution injection nozzle 2,a pressurized air supply pump (compressor) 6, a pressurized air valve 8,a urea solution supply pump 9, a switching valve 11, a control device14, a temperature sensor 12, a humidity sensor 13, a first supply flowpath 15, a second supply flow path 16, a NOx catalyst 19 and the like.

The urea solution injection nozzle 2 supplies a urea solution to aninside of the exhaust pipe 21. The urea solution injection nozzle 2includes a tubular member, and one of sides (lower side) thereof isinserted into the inside of the exhaust pipe 21 from the outside. Theurea solution injection nozzle 2 has a double pipe 3, a liquid nozzle 4,an air nozzle 5 and the like (see FIG. 2).

The pressurized air supply pump (compressor) 6 supplies pressurized air.The pressurized air supply pump 6 pressurizes (compresses) air andsupplies the air. The pressurized air supply pump 6 supplies the air toan air tank 7 when a pressure of the air tank 7 becomes lower than apredetermined pressure, and stops when the pressure of the air tank 7reaches the predetermined pressure. In this embodiment, the pressurizedair supply pump 6 is not limited and may be a member which can maintainthe pressure of the air tank 7.

The pressurized air valve 8 opens and closes a flow path of thepressurized air. The pressurized air valve 8 is provided in the secondsupply flow path 16. The pressurized air valve 8 includes anelectromagnetic valve and a solenoid thereof is connected to the controldevice 14. The pressurized air valve 8 can be switched to a position Vand a position W by sliding a spool. When the pressurized air valve 8 isat the position V, the second supply flow path 16 is closed. Then, thepressurized air is not supplied to the urea solution injection nozzle 2.When the pressurized air valve 8 is at the position W, the second supplyflow path 16 is opened. Then, the pressurized air is supplied to theurea solution injection nozzle 2. The pressurized air valve 8 is notlimited thereto and may alternatively be held at the position V or theposition W by a driving motor or the like.

The urea solution supply pump 9 supplies a urea solution. The ureasolution supply pump 9 is provided in the first supply flow path 15. Theurea solution supply pump 9 supplies the urea solution in a ureasolution tank 10 via the first supply flow path 15 to the urea solutioninjection nozzle 2 at a predetermined flow rate. In this embodiment, theurea solution supply pump 9 is not limited and may be a member which cansupply the urea solution at the predetermined flow rate.

The switching valve 11 switches a flow path of the urea solution. Theswitching valve 11 is provided at the downstream side of the ureasolution supply pump 9 in the first supply flow path 15. A drain pot 17is connected via a flow path 15 a to the switching valve 11. Theswitching valve 11 includes an electromagnetic valve and a solenoidthereof is connected to the control device 14. The switching valve 11can be switched to a position X and a position Y by sliding a spool.

When the switching valve 11 is at the position X, the first supply flowpath 15 is closed and the urea solution injection nozzle 2 iscommunicated with the drain pot 17. Then, the urea solution is notsupplied to the urea solution injection nozzle 2, and the urea solutionin the first supply flow path 15 and the urea solution injection nozzle2 at the downstream side of the switching valve 11 is discharged to thedrain pot 17.

When the switching valve 11 is at the position Y, the first supply flowpath 15 is opened. Then, the urea solution is supplied to the ureasolution injection nozzle 2.

The temperature sensor 12 detects a temperature T of the atmosphere. Thetemperature sensor 12 is arranged at a position such as an engine roomof a ship at which the temperature T of the atmosphere sucked by theengine 20 can be detected. This embodiment is not limited thereto, andany means is available if it can detect the temperature T of theatmosphere and transmit a detection signal of the temperature to thecontrol device 14.

The humidity sensor 13 detects an absolute humidity H of the atmosphere.The humidity sensor 13 is arranged at a position such as the engine roomof the ship at which the absolute humidity H of the atmosphere sucked bythe engine 20 can be detected. This embodiment is not limited thereto,and any means is available if it can detect the absolute humidity H andtransmit a detection signal of the absolute humidity to the controldevice 14. For example, it may alternatively be configured that arelative humidity is detected and a detection signal thereof istransmitted to the control device 14 so as to calculate the absolutehumidity H based on the temperature T of the atmosphere.

The control device 14 controls the urea solution supply pump 9, theswitching valve 11, the pressurized air valve 8 and the like. Variousprograms and data for controlling the urea solution supply pump 9, theswitching valve 11, the pressurized air valve 8 and the like are storedin the control device 14. The control device 14 may be configured byconnecting a CPU, a ROM, a RAM, a HDD and the like by a bus, or mayalternatively be configured by a one-chip LSI or the like. The controldevice 14 may be configured integrally with an ECU 22 which controls theengine 20.

A map M is stored in the control device 14. The map M converts an actualNOx discharge amount, which is an amount of NOx included in exhaust gasof the engine 20 driven with each rotation speed and each load underpredetermined temperature and absolute humidity of the atmosphere, intoa standard NOx discharge amount Ns, which is an amount of NOx with eachrotation speed and each load under standard conditions (for example,10.71 g/kg 25° C.), with a correction formula F which is known or ameasured formula. Concretely, the actual NOx discharge amount of theengine 20 with optional rotation speed and load under the predeterminedtemperature and absolute humidity of the atmosphere is measured undereach driving condition. Then, the actual NOx discharge amount isconverted into the standard NOx discharge amount Ns under the standardconditions with the correction formula F based on temperature andabsolute humidity of the atmosphere at the time of the measurement. Themap M of the standard NOx discharge amount Ns made as the above isstored. In addition, the correction formula F is stored in the controldevice 14.

The control device 14 is connected to the solenoid of the pressurizedair valve 8 and can control opening and closing of the pressurized airvalve 8.

The control device 14 is connected to a driving motor of the ureasolution supply pump 9 and can control an operation state of the ureasolution supply pump 9. Namely, by controlling the operation state ofthe urea solution supply pump 9, the control device 14 can changeoptionally an addition amount Q of the urea solution added to theexhaust gas. The control device 14 is connected to the solenoid of theswitching valve 11 and can control opening and closing of the switchingvalve 11.

The control device 14 is connected to the temperature sensor 12 and canobtain a signal of the temperature T of the atmosphere detected by thetemperature sensor 12. The control device 14 is connected to thehumidity sensor 13 and can obtain a signal of the absolute humidity H ofthe atmosphere detected by the humidity sensor 13. A relative humiditycan be detected and a detection signal thereof can be transmitted to thecontrol device 14 so as to calculate the absolute humidity with thecontrol device 14 using the temperature T of the atmosphere.

The control device 14 is connected to the ECU 22 and can obtain variouskinds of information about the engine 20 obtained by the ECU 22.Concretely, the control device 14 can obtain a rotation speed R of theengine 20, which is detected by a rotation speed sensor 20 a of theengine 20, via the ECU 22. The control device 14 can obtain an output ofa dynamo 23, driven by the engine 20, detected by a load sensor 23 a ofthe dynamo 23 as a load L of the engine 20 via the ECU 22. The load L isnot limited to the detection value of the load sensor 23 a and mayalternatively be calculated from a rack position, a fuel injectionamount or an actual rotation speed. The control device 14 may obtainvarious kinds of information about the engine 20 directly not via theECU 22.

The control device 14 is connected to an input device (not shown) andcan obtain a signal about a target purification rate inputted from theinput device and concentration of the urea solution. Alternatively,information about the target purification rate and the concentration ofthe urea solution can be inputted and defined previously.

The NOx catalyst 19 promotes deoxidization reaction of NOx. The NOxcatalyst 19 is arranged inside the exhaust pipe 21 and at the downstreamside of the urea solution injection nozzle 2. The NOx catalyst 19 isconfigured honeycomb like and promotes reaction that ammonia generatedby thermal hydrolysis of the urea solution reduces NOx included in theexhaust gas into nitrogen and water.

Next, an explanation will be given on the urea solution injection nozzle2 of internal mixing type concretely referring to FIG. 2. The type ofthe urea solution injection nozzle 2 is not limited to this embodimentand an external mixing type urea solution injection nozzle mayalternatively be used. A fluid nozzle used for an air-less type exhaustpurification apparatus which does not use pressurized air mayalternatively be used.

As shown in FIG. 2, the urea solution injection nozzle 2 has the doublepipe 3, the liquid nozzle 4, the air nozzle 5, and the like.

The double pipe 3 is a main component of the urea solution injectionnozzle 2 and constitutes the flow path of the urea solution and the flowpath of the pressurized air. One of sides of the double pipe 3 isarranged inside the exhaust pipe 21 and the other side (upstream side)thereof is arranged outside the exhaust pipe 21. The downstream end ofthe double pipe 3 is arranged upstream the NOx catalyst 19 arrangedinside the exhaust pipe 21.

The double pipe 3 includes an outer pipe 3 b and an inner pipe 3 aarranged inside the outer pipe 3 b. A urea solution flow path 3 c whichis a flow path of the urea solution is configured in the inner pipe 3 a.A gas flow path 3 d which is a flow path of the pressurized air isconfigured in a space between the inner pipe 3 a and the outer pipe 3 b.In a middle part of an outer side of the outer pipe 3 b, a connectionpart (not shown) which can be connected watertightly to the exhaust pipe21 is configured. In downstream ends of the inner pipe 3 a and the outerpipe 3 b, a female screw part 3 e and a male screw part 3 f are formedrespectively. In an upstream end of the double pipe 3, a urea solutionsupply port 3 g communicated with the urea solution flow path 3 c and agas supply port 3 h communicated with the gas flow path 3 d areconfigured.

The liquid nozzle 4 injects the urea solution. The liquid nozzle 4 isformed by a substantially cylindrical member and arranged downstream thedouble pipe 3. One of ends (downstream end) of the liquid nozzle 4 isformed conically around the axis. At a center of the end, a projectionpart 4 a which is substantially cylindrical is formed so as to beprojected axially. In the other end (upstream end) of the liquid nozzle4, a male screw part 4 b is formed so as to be projected axially.Furthermore, in an axial center part of the liquid nozzle 4, a ureasolution flow path 4 c is formed so as to penetrate axially the wholeliquid nozzle 4 from the male screw part 4 b to the projection part 4 a.A middle part of the urea solution flow path 4 c is contracteddiametrically so that an inner diameter of a downstream end of the ureasolution flow path 4 c is formed smaller than an inner diameter of anupstream end of the urea solution flow path 4 c.

The male screw part 4 b of the liquid nozzle 4 is screwed to the femalescrew part 3 e of the double pipe 3. Accordingly, the double pipe 3 isconnected to the liquid nozzle 4 and the urea solution flow path 4 c iscommunicated with the urea solution flow path 3 c of the double pipe 3.Then, the urea solution can be supplied from the urea solution flow path3 c of the double pipe 3 to the urea solution flow path 4 c.

The air nozzle 5 injects the urea solution which is atomized. The airnozzle 5 is formed by a substantially cylindrical member. The air nozzle5 is arranged downstream the liquid nozzle 4 so that one of ends(upstream end) of the air nozzle 5 touches the downstream end of thedouble pipe 3. A flange part 5 a is firmed in a side surface of anupstream end of the air nozzle 5. In an axial part of the air nozzle 5,a hole which has a substantially conical diametrical contracted partcontracted diametrically from a middle part toward the other side(downstream side) is formed penetratingly from the upstream end to thedownstream end. An inner diameter of an upstream end of the hole isformed enough for the pressurized air to pass therethrough even if adownstream end of the liquid nozzle 4 is inserted into the upstream endof the hole. In an axial center part of a diametrical contracted sideend of the diametrical contracted part, a mixing flow path 5 c of theurea solution is formed. In a downstream end of the air nozzle 5, aninjection port 5 e which is an opening of the mixing flow path 5 c isformed.

The air nozzle 5 is connected to the double pipe 3 by a nut 5 b. Thedownstream end of the liquid nozzle 4 is inserted into the hole of theupstream side of the air nozzle 5 (the mixing flow path 5 c). At thistime, a space is formed between the hole of the air nozzle 5 and theliquid nozzle 4. The space is communicated as a gas flow path 5 d withthe gas flow path 3 d of the double pipe 3 and the mixing flow path 5 c.Accordingly, the urea solution is supplied from the urea solution flowpath 4 c of the liquid nozzle 4 to the mixing flow path 5 c, and thepressurized air is supplied from the gas flow path 5 d to the mixingflow path 5 c. Namely, the injection port 5 e can inject the ureasolution by screwing the air nozzle 5 to the double pipe 3.

According to the above, the urea solution injection nozzle 2 has theliquid nozzle 4 which injects the urea solution toward one of the sides(downstream side) and the air nozzle 5, and injects the urea solutiontoward the NOx catalyst 19. In this embodiment, in the urea solutioninjection nozzle 2, the urea solution flow path 4 c, the gas flow path 5d, and the mixing flow path 5 c are configured by the liquid nozzle 4and the air nozzle 5. However, the configuration is not limited theretoand the urea solution flow path 4 c, the gas flow path 5 d, and themixing flow path 5 c may be configured respectively.

An explanation will be given on an operation mode of the pressurized airvalve 8 and the switching valve 11 referring to FIG. 1.

As shown in FIG. 1, the air tank 7 is connected to the gas supply port 3h of the urea solution injection nozzle 2 via the pressurized air valve8 by the second supply flow path 16.

As mentioned above, normally, the pressurized air valve 8 is held at theposition V. In this case, since the second supply flow path 16 isclosed, the pressurized air is not supplied to the gas supply port 3 hof the urea solution injection nozzle 2.

When the control device 14 energizes the solenoid of the pressurized airvalve 8, the pressurized air valve 8 is switched from the position V tothe position W. In this case, since the second supply flow path 16 isopened, the pressurized air is supplied to the gas supply port 3 h ofthe urea solution injection nozzle 2.

When the control device 14 stops the energization to the solenoid of thepressurized air valve 8, the pressurized air valve 8 is switched to theposition V. In this case, since the second supply flow path 16 isclosed, the pressurized air is not supplied to the gas supply port 3 hof the urea solution injection nozzle 2.

As shown in FIG. 1, the urea solution tank 10 is connected to the ureasolution supply port 3 g of the urea solution injection nozzle 2 via theurea solution supply pump 9 and the switching valve 11 by the firstsupply flow path 15.

As mentioned above, normally, the switching valve 11 is held at theposition X. In this case, since the first supply flow path 15 is closed,the urea solution is not supplied to the urea solution supply port 3 gof the urea solution injection nozzle 2. The urea solution supply port 3g of the urea solution injection nozzle 2 is atmosphere-opened in thedrain pot 17 via the flow path 15 a.

When the control device 14 energizes the solenoid of the switching valve11, the switching valve 11 is switched to the position Y. In this case,since the first supply flow path 15 is opened, the urea solution issupplied to the urea solution supply port 3 g of the urea solutioninjection nozzle 2. Since the communication with the drain pot 17 is cutoff, the urea solution supply port 3 g of the urea solution injectionnozzle 2 is not atmosphere-opened.

When the control device 14 stops the energization to the solenoid of theswitching valve 11, the switching valve 11 is switched to the positionX. In this case, since the first supply flow path 15 is closed, the ureasolution is not supplied to the urea solution supply port 3 g of theurea solution injection nozzle 2. Since the communication with the drainpot 17 is permitted, the urea solution supply port 3 g of the ureasolution injection nozzle 2 is atmosphere-opened in the drain pot 17.

An explanation will be given on an operation mode of the urea solutioninjection nozzle 2 referring to FIGS. 1 and 2.

As shown in FIG. 1, when the supply (injection) of the urea solution tothe inside of the exhaust pipe 21 is started, the control device 14switches the switching valve 11 to the position Y so that the ureasolution is supplied to the urea solution supply port 3 g of the ureasolution injection nozzle 2 (the double pipe 3). The urea solution isinjected from the projection part 4 a of the liquid nozzle 4 to themixing flow path 5 c of the air nozzle 5 via the urea solution flow path3 c of the double pipe 3 and the urea solution flow path 4 c of theliquid nozzle 4.

In this state, the control device 14 switches the pressurized air valve8 to the position W so that the pressurized air is supplied to the gassupply port 3 h of the urea solution injection nozzle 2 (the double pipe3). As shown in FIG. 2, the pressurized air is injected at apredetermined pressure via the gas flow path 3 d of the double pipe 3and the gas flow path 5 d of the air nozzle 5 to the mixing flow path 5c of the air nozzle 5. As a result, the urea solution collides with thepressurized air inside the mixing flow path 5 c of the air nozzle 5 andis atomized, and then injected via the injection port 5 e of the airnozzle 5.

As shown in FIG. 1, when the supply (injection) of the urea solution tothe inside of the exhaust pipe 21 is stopped, the control device 14switches the switching valve 11 to the position X so that the supply ofthe urea solution to the urea solution supply port 3 g of the ureasolution injection nozzle 2 (the double pipe 3) is stopped. Accordingly,the urea solution supply port 3 g of the double pipe 3 isatmosphere-opened via the first supply flow path 15 and the switchingvalve 11.

An explanation will be given on a mode of calculation of the additionamount of the urea solution referring to FIG. 3.

The control device 14 obtains the signal of the temperature T of theatmosphere from the temperature sensor 12 and obtains the signal of theabsolute humidity H of the atmosphere from the humidity sensor 13. Thecontrol device 14 obtains the signal of the rotation speed R of theengine 20 from the rotation speed sensor 20 a and obtains the signal ofthe load L of the engine 20 from the load sensor 23 a. The controldevice 14 calculates an actual NOx discharge amount Nr based on theobtained information and controls the operation state of the ureasolution supply pump 9 (see FIG. 1).

As shown in FIG. 3, the control device 14 controls the operation stateof the urea solution supply pump 9 with below steps.

Firstly, at a step S110, the control device 14 obtains the signal of thetemperature T of the atmosphere from the temperature sensor 12 andobtains the signal of the absolute humidity H of the atmosphere from thehumidity sensor 13. The control device 14 obtains the signal of therotation speed R of the engine 20 from the rotation speed sensor 20 aand obtains the signal of the load L of the engine 20 from the loadsensor 23 a.

At a step S120, the control device 14 calculates the standard NOxdischarge amount Ns, which is an amount of NOx discharged from theengine 20 driven with the rotation speed R and the signal of the load Lunder standard conditions, from the signal of the rotation speed R andthe signal of the load L of the engine 20 with the map M.

At a step S130, the control device 14 calculates an actual NOx dischargeamount Nr, which is an amount of NOx discharged from the engine 20driven with the rotation speed R and the signal of the load L under thetemperature T and the absolute humidity H of the atmosphere, from thestandard NOx discharge amount Ns corresponding to the rotation speed Rand the signal of the load L calculated at the step S120 and the signalof the temperature T and the signal of the absolute humidity H of theatmosphere with the correction formula F by inverse operation. Namely,the actual NOx discharge amount Nr which is necessary to set the amountof NOx discharged from the engine 20, which is driven with the rotationspeed R and the signal of the load L under the temperature T and theabsolute humidity H of the atmosphere, to the standard NOx dischargeamount Ns is calculated with the correction formula F.

At a step S140, the control device 14 determines the addition amount Qof the urea solution, which is necessary to reduce the actual NOxdischarge amount Nr from the target purification rate and theconcentration of the urea solution which are set optionally.

At a step S150, the control device 14 controls the operation state ofthe urea solution supply pump 9 so as to supply the addition amount Q ofthe urea solution in the urea solution supply pump 9 to the exhaust gas.Subsequently, the control device 14 returns to the step S110.

Accordingly, as shown in FIG. 4, in the case in which the additionamount Q of the urea solution is Q1 while the actual NOx dischargeamount Nr is Nr1, when the actual NOx discharge amount Nr is decreasedto Nr2′, NOx is decreased more than the target purification rate (atwo-dot chain line in FIG. 4) (over-denitration) (see A′). Then, by theabove control, the decrease of the actual NOx discharge amount Nr toNr2′ is calculated, and the urea solution supply pump 9 is controlled soas to set the addition amount Q of the urea solution to a suitableaddition amount Q2′. Furthermore, when the actual NOx discharge amountNr is decreased to Nr2, NOx is decreased more than the targetpurification rate (over-denitration) and ammonia exceeding a theoreticalequivalent (a dashed line in FIG. 4) and remaining is discharged outsidethe exhaust pipe 21 (ammonia slip). Then, by the above control, thedecrease of the actual NOx discharge amount Nr to Nr2 is calculated, andthe urea solution supply pump 9 is controlled so as to set the additionamount Q of the urea solution to a suitable addition amount Q2. When theactual NOx discharge amount Nr is increased to Nr3, denitration shortagethat NOx cannot be decreased to the target purification rate occurs (seea point B). Then, by the above control, the increase of the actual NOxdischarge amount Nr to Nr3 is calculated, and the urea solution supplypump 9 is controlled so as to set the addition amount Q of the ureasolution to a suitable addition amount Q3.

As the above, the exhaust purification apparatus 1, in which ammonia isadded as a reducing agent to the exhaust gas of the engine 20 which isan internal combustion engine so as to reduce nitrogen oxide in theexhaust gas, has the temperature sensor 12 detecting a temperature T ofthe atmosphere, the humidity sensor 13 detecting the absolute humidity Hor the relative humidity of the atmosphere, and the control device 14calculating the addition amount of the urea solution. The map M, whichconverts the actual NOx discharge amount Nr of the engine 20 driven witheach rotation speed and each load under predetermined temperature andabsolute humidity of the atmosphere into the standard NOx dischargeamount Ns of the engine 20 with each rotation speed and each load underthe standard conditions with the correction formula F is stored in thecontrol device 14. The rotation speed sensor 20 a which is a rotationspeed detection means detecting the rotation speed of the engine 20 andthe load sensor 23 a of the dynamo 23 which is a load detection meansdetecting the load of the engine 20 are connected to the control device14. The standard NOx discharge amount Ns corresponding to the rotationspeed R detected by the rotation speed sensor 20 a and the load Ldetected by the load sensor 23 a is calculated with the map M. Thestandard NOx discharge amount Ns is converted into the actual NOxdischarge amount Nr of the rotation speed R and the load L under thetemperature T of the atmosphere detected by the temperature sensor 12and the absolute humidity H of the atmosphere detected by the humiditysensor 13 with the correction formula F by inverse operation. Theaddition amount Q of the urea solution is calculated based on the actualNOx discharge amount Nr.

According to the configuration, the actual NOx discharge amount Nr basedon the characteristic of the engine 20 can be calculated whileconsidering the temperature T of the atmosphere and the absolutehumidity H of the atmosphere which influence the NOx discharge amountgreatly. Accordingly, the urea solution of the suitable amount can beadded without measuring directly the actual NOx discharge amount Nr witha NOx sensor.

The addition amount Q is calculated in consideration of the targetpurification rate and the concentration of the urea solution.

According to the configuration, the addition amount Q can be adjustedcorresponding to the operating condition. Accordingly, the urea solutionof the suitable amount can be added without measuring directly theactual NOx discharge amount Nr with a NOx sensor.

INDUSTRIAL APPLICABILITY

The present invention can be used especially for an exhaust purificationapparatus for a ship.

DESCRIPTION OF NOTATIONS

-   -   1 exhaust purification apparatus    -   12 temperature sensor    -   13 humidity sensor    -   14 control device    -   20 engine    -   20 a rotation speed sensor    -   23 a load sensor    -   R rotation speed    -   W load    -   Ns standard NOx discharge amount    -   Nr actual NOx discharge amount    -   Q addition amount

1. An urea solution injection device of an exhaust purification devicein which an urea solution is added as a reducing agent to exhaust gas ofan internal combustion engine so as to reduce nitrogen oxide in theexhaust gas, comprising: a temperature sensor detecting a temperature ofatmosphere; a humidity sensor detecting an absolute humidity or arelative humidity of the atmosphere; and a control device calculating anaddition amount of the urea solution, characterized in that a map, whichconverts an actual NOx discharge amount of the internal combustionengine driven with each rotation speed and each load under predeterminedtemperature and absolute humidity of the atmosphere into the standardNOx discharge amount of the internal combustion engine with eachrotation speed and each load under standard conditions with a correctionformula is stored in the control device, a rotation speed detectionmeans detecting the rotation speed of the internal combustion engine anda load detection means detecting the load of the internal combustionengine are connected to the control device, and the standard NOxdischarge amount corresponding to the rotation speed detected by therotation speed detection means and the load detected by the loaddetection means is calculated with the map, the standard NOx dischargeamount is converted into the actual NOx discharge amount of the rotationspeed and the load under the temperature of the atmosphere detected bythe temperature sensor and the absolute humidity of the atmospheredetected by the humidity sensor with the correction formula by inverseoperation, and the addition amount of the urea solution is calculatedbased on the actual NOx discharge amount.
 2. The urea solution injectiondevice according to claim 1, wherein the addition amount is calculatedin consideration of a target purification rate and a concentration ofthe urea solution.